While success in high-speed motor sports is commonly attributed to driver skill, the proper set-up of a race vehicle is also an important factor. Consequently, both prior to and during a race, many aspects of a vehicle are subject to scrutiny and adjustment based on track conditions, driver perception, weather conditions, or even the skill level of competitors. Particular attention is paid to the elements of the suspension system of a vehicle, since these elements directly affect the driver's control over the vehicle.
Numerous types of suspension configurations are currently in use in modern vehicles. One common configuration includes upper and lower control arms which support a knuckle between them. The control arms are typically rigid members which may be stamped from steel or cast from another metal. A spring and shock absorber are typically connected to a portion of the lower control arm and to the vehicle's frame so as to provide a particular spring rate (a ratio which describes how resistant a spring is to being compressed or expanded during the spring's deflection) and to control the movement of the wheel supported on the knuckle.
The geometry of the upper and lower control arms has a direct effect on such important parameters as wheel camber (the angle of the wheel relative to a vertical axis, as viewed from the front or the rear of the vehicle), wheel caster (the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side of the vehicle) and toe (the angle to which the wheels are out of parallel), all of which have a significant impact on vehicle performance. For example, toe settings affect tire wear, straight-line stability, and the corner entry handling characteristics of the vehicle.